1. Field of the Invention
This invention relates to a fuel injection timing control system for an internal combustion engine, such as a diesel engine, and more particularly to a control system of the closed-loop or feed-back type employing a hydraulically-driven device.
2. Description of the Prior Art
In diesel engines, fuel injection timing needs to be adjusted to match changes in engine rotational speed (rpm) and engine load to achieve optimal engine performance. Closed-loop or feed-back control systems are conventionally used for accurate and stable control. Generally, the closed-loop control system becomes less stable as the response time thereof decreases. Accordingly, a compromise is necessary in setting the response time and the stability of the system.
Some closed-loop control systems for fuel injection timing employ hydraulic devices. The speed of force transmission, i.e., response, of these hydraulic devices depends on the conditions of the working fluid, such as temperature and pressure thereof. As a result, the response time and thus the stability of the over-all closed-loop control system also depends on the conditions of the working fluid. It is, therefore, difficult to keep the characteristics of the system constant as the conditions of working fluid change.